The present invention relates to a method of manufacturing a dental prosthesis by utilizing a CAD/CAM device. Also, the present invention relates to a method and device for placing an object so that an objective surface of the object does not overhang when a surface shape of the object is measured.
An attempt has been made to introduce a method of manufacturing a dental prosthesis by using the technique of CAD/CAM into the field of dentistry. In order to obtain a prosthetic shape from the oral cavity, a means for obtaining the prosthetic shape by taking an impression model is effective although it is apparently complicated because it is a method, as a usually adopted dental technical means, by which a precise shape of a dental prosthesis is obtained in a short period of time.
On the other hand, the calculating capacity of a computer has been enhanced and further the price has been reduced, the techniques of CAD/CAM have come into wide use, and manufacturing a dental prosthesis by utilizing the combination of the technique of CAD/CAM has come into practical use.
In this connection, in the case where a dental prosthesis for a small decayed portion of a tooth such as an inlay is manufactured, it is possible to directly mold the decayed portion of the tooth and take it out as a model. However, since the shape of such a dental prosthesis is indefinite, even if the small decayed portion is molded and taken out as a model, it is necessary to mark a contact margin portion coming into contact with a tooth and also it is necessary to mark a portion which becomes a surface of the tooth. Since the dental prosthesis concerned is very small and its shape is indefinite, it is complicated to directly measure the surface of the dental prosthesis.
As a method of making a three-dimensional measurement of an object, there are provided a laser beam method, a contact method, a gray scale method, a moire method and so forth. However, when the measurement is made in one direction, if the object has an overhang portion, it is impossible to measure a portion shaded by the overhang portion. In this case, the overhang portion means a portion which protrudes in a direction perpendicular to the measuring direction.
In order to obtain information which cannot be obtained from the portion shaded by the overhang portion, there is provided a method in which multiple axes are manually or automatically controlled. However, actually, the adjusting axes, ranges and units are limited. Therefore, it is necessary to place the object at a position and also it is necessary to place the object in a direction so that the object can be measured under the above conditions. This important work must be manually conducted, which is complicated and difficult.
In the case of using a measurement device, the degree of freedom of which is high, the accuracy is usually low. In the case of using a measurement device, both the accuracy and the degree of freedom of which are high, the cost is increased.
In the case where an object is measured in one direction, it is necessary to place the object so that an overhang portion cannot be created. In this case, the overhang portion means a portion located at the rear of a protruding portion in a direction perpendicular to the measuring direction. However, in the case of an object, the shape of which is horizontal with respect to the measuring direction, or the shape of which is oblique and is close to the horizontal shape, it is difficult to manually place the object so that the overhang portion cannot be created. It can be considered that even if the overhang portion is created, it is impossible to discriminate the overhang portion from other portions and a measurement is executed as it is.
It is an object of the present invention to provide a method of manufacturing a dental prosthesis capable of providing a dental prosthesis, the shape of which is indefinite, with high accuracy.
It is another object of the present invention to provide a method of placing an object for measurement and a measuring device capable of accurately measuring an object to be measured which may have an overhang portion.
In order to accomplish the above object, the present invention provides a method of obtaining shape measuring data of a dental prosthesis while consideration is given to machining the dental prosthesis by CAD/CAM.
That is, first, data of a natural tooth having a decayed portion are obtained from an impression model. After that, a temporary filler is charged into this impression model, and data of the entire tooth after prosthetic treatment are obtained. Then, these two sets of data are differentially synthesized in the same coordinate space so as to obtain a shape of the dental prosthesis.
According to this method, the calculation of a difference can be executed while attaching an importance to one of three directions, and the amount of calculation can be reduced. That is, the surface after the completion of prosthetic treatment is smooth in many cases. In this case, it is possible that the surface is assumed to be on a plane formed by axes of X and Y. On the other hand, data of the decayed portion may be assumed to be data in the direction of Z-axis. Therefore, it is possible to concentrate the calculation upon one coordinate in the three dimensional coordinates.
Further, since the data are based on the surface data of the tooth which has been subjected to dental prosthetic treatment, the margin line and the surface portion of the tooth can be easily recognized.
Due to the foregoing, when the dental prosthesis is machined, a position of the connector for connecting the machining device with the machining block can be automatically grasped, and a space in which adhesive is coated can be easily formed.
When the connector is mounted on the surface, the dental prosthesis and the natural tooth can be connected to each other without being affected by the connector. The remnants produced when the connecting rib and the dental prosthesis are separated from each other after the completion of machining can be easily cut off and adjusted.
The present invention provides a method of forming data used when a dental prosthesis, the shape of which is indefinite, such as an inlay is measured and the dental prosthesis concerned is machined. On the assumption that the data are formed, an organized decayed tooth portion, into which a dental prosthesis is introduced, is formed.
A model of a shape of a decayed tooth portion is made of plaster by a conventional method.
Data of a surface shape of the model are obtained.
Concerning the means for obtaining the surface shape data, there are provided a means for obtaining digital data by contact scanning on the surface conducted by a contact probe, an optical means in which laser beams are used, and a means for obtaining digital data by using ultrasonic waves or photographs. In order to obtain highly accurate surface shape data, it is preferable to adopt a means in which the contact probe is used.
A decayed portion of the decayed tooth portion model is prosthetically treated, and a tooth shape model having a surface after the completion of prosthetic treatment is obtained.
Surface data of the tooth shape model are obtained by the above method.
Measuring a tooth model of a predetermined size stably as described above is easier than directly measuring an indefinite dental prosthesis shape.
Three dimensional coordinates are set on the basis of the surface data concerned. Alternatively, the surface data are converted onto the common three dimensional coordinates.
In this connection, the surface data are not necessarily provided with a flatness property in a portion to be prosthetically treated. Further, it is not necessary for the surface data to have a flatness property in a portion to be prosthetically treated.
The decayed tooth shape portion model is converted into three dimensional data so that the model can be matched with the surface data from the positional viewpoint. In this case, a portion which changes from a position at which both data coincide with each other becomes boundary data (margin line) between the natural tooth and the dental prosthesis, and data showing the dental prosthesis shape is formed. The change may be determined by whether the data exist or not. However, since errors may be caused in the values in some cases, it is possible to provide a process in which it is judged that the dental prosthesis portion exists when a change is caused in a unit distance and this change continues by a predetermined number of times.
Plane coordinates caused by the surface data on the three-dimensional coordinates are made into a unit matrix, and a difference between the surface data corresponding to it and the surface profile data of a decayed portion for each unit is calculated, or a summation of the surface data corresponding to it and the surface profile data of a decayed portion for each unit is calculated. In this way, numeric values necessary for machining are obtained.
When the thickness of a dental prosthesis in the periphery of a boundary portion is measured and the measured thickness is not sufficiently large, this portion may be erased and the boundary portion may be corrected.
This correction may be arbitrarily visually made by a display, in the case of connection of a dental prosthesis shape, virtually displayed on a display according to the above data and a decayed tooth portion shape. Alternatively, this correction may be made by process in which every portion is equally erased.
A correction is made according to the boundary line concerned so that a space (offset) in which adhesive is coated in the periphery of the dental prosthesis data can be provided.
A connecting position of a rib for machining is determined from the surface data. It is preferable that the connecting position concerned is determined so that it is not contacted with the margin line. Even if the connecting position concerned is contacted with the margin line, it is preferable to determine the connecting position so that the contact length can be minimized.
In the method of placing an object for measurement and the measuring device of the present invention, while the system is not greatly changed, the same state as that of measurement is adopted when the object is placed so that an overhang portion cannot be created. In this way, the object is placed and fixed. Due to the foregoing, an essential and important work of measurement, which is visually and manually conducted in the prior art or conducted by a highly sophisticated system, can be simply and positively conducted. As a measurement system, it is sufficient that a limited function is provided. Therefore, it is possible to put it into a wide use and further the cost can be reduced.
In the present invention, in the case where a measurement object placing section is set to be a horizontal plane, the measurement object is moved so that a vertical face of the measurement object can coincide with a vertical side of an adjusting member and this state can be fixed.
For example, the side of the adjusting member is contacted with the vertical face of an object to be measured and fixed by a holder so that the state can be temporarily held. An example of the holder is a jig by which a changed state of the measurement object can be fixed as it is when the adjusting member and the vertical face coincide with each other.
The adjusting member can be substituted by a probe for measuring the profile of the measurement object when the probe itself has such a vertical face. In this connection, when at least the side of the adjusting member or the face originated from the side of the probe can be kept vertical or adjusted to be vertical, after the measurement object has been held on the side of the probe, the state may be adjusted so that the measurement object placing section can be placed with respect to the face of the measurement object.
In this connection, the present invention is effectively utilized for a measuring and machining device for a dental prosthesis such as an artificial root of a tooth having a large number of indefinite measurement objects and further having a large number of vertical and horizontal portions.